Last word on the Big Bang.

Interdisciplinary science discussions. Also, if you are not sure where to place your thread, please post it here.

Re: Last word on the Big Bang.

Postby TheVat on December 31st, 2020, 1:24 pm 

Is there a conservation of energy problem there? The "lost" energy of the photon (it can't slow down, so it has to shift red) is actually contained in the increasing volume of space?
User avatar
TheVat
Forum Administrator
 
Posts: 7854
Joined: 21 Jan 2014
Location: Black Hills


Re: Reflecting on Energy Conservation

Postby Faradave on December 31st, 2020, 4:40 pm 

TheVat wrote:Is there a conservation of energy problem there? The "lost" energy of the photon (it can't slow down, so it has to shift red) is actually contained in the increasing volume of space?
That's a good question. Things get confusing with dark energy, which acts like negative gravity. Here's how I think of it.

When you throw a ball up from earth it slows, losing kinetic energy (KE), while gaining potential energy (PE) of altitude. At some point it stops and the process reverses as it returns. I think of light's "radiant energy" (E=hf) analogous to KE of massive objects.

Similarly, light looses KE (gets redshifted) climbing out of a gravity well. But if you reflect it back with a mirror, it will regain KE (blueshift) on the return trip. So, light effectively gains PE as it looses KE climbing out of a gravity well.

Light leaving a distant galactic cluster, because of expansion, finds itself at a higher altitude from its emitter, than if there was no expansion. If we absorb it redshifted, it should still be the case that our system now has the energy of that low KE photon at a higher altitude (PE) above its source galaxy than it would have been without expansion.

Still, I think it may be too soon to rigorously include dark energy in our conservation laws.
User avatar
Faradave
Resident Member
 
Posts: 2009
Joined: 10 Oct 2012
Location: Times Square (T2)


Previous

Return to Anything Science

Who is online

Users browsing this forum: No registered users and 10 guests